Hydraulic and Environmental Performance of Aerating Turbine …hydroppi.com/uploads/3/4/5/6/34564986/hydraulic_and... · 2018. 9. 28. · Hydraulic and Environmental Performance of

Hydraulic and Environmental Performance of Aerating TurbineTechnologies

by

Patrick MarchPrincipal Consultant, Hydro Performance Processes Inc.

[email protected]; 865.603.0175

Abstract

EPRI’s 2002 report, Maintaining and Monitoring Dissolved Oxygen at HydroelectricProjects: Status Report (1005194) provided a comprehensive review of a wide rangeof techniques and technologies for improving the dissolved oxygen (DO) levels inreleases from hydroelectric projects. Aerating turbine technologies have beendeveloped and demonstrated by multiple turbine manufacturers. These technologiescan provide higher generation efficiency, higher capacity, and improvedenvironmental performance. However, aerating turbine technologies have not beenwidely implemented, in part due to insufficient information on, and industryunderstanding of, the life-cycle costs and benefits from the technologies. This paperis based on a December 2009 EPRI report, Technology Update on Aerating Turbines[March, 2009]. The 2009 report and this paper supplement the 2002 EPRI report andfocus primarily on aerating turbine technologies for new turbine installations andturbine upgrades. Limited information on performance of retrofitted aeration systemsis also presented for comparison purposes.

Turbine manufacturers, utilities, and agencies provided information and performancedata for aerating turbine technologies. Specific industry examples are examined andpresented as case studies, with an emphasis on hydraulic performance (turbineefficiency with and without aeration, turbine capacity increases) and environmentalperformance (air flows and DO increases). The paper discusses the development ofaerating turbine technologies, describes some of the difficulties in assessing theperformance of aerating turbines, provides detailed case studies for three aeratingturbine technologies (central aeration, peripheral aeration, and distributed aeration),discusses the implications of the case study results for plant operation andoptimization, and makes recommendations for additional related research.

1. INTRODUCTION

Overview of Aeration

Impoundments and flow releases from hydropower facilities can adversely impact theaquatic life upstream, downstream, and passing through the sites. In the United States,regional environmental concerns include the improvement of dissolved oxygen (DO)levels to protect aquatic habitat in tailwaters below dams.

Hydropower projects likely to experience problems with low DO include those with areservoir depth greater than 15 m, power capacity greater than 10 MW, reservoir volumegreater than 6.1 x 107 m3, densimetric Froude number less than 7, and a retention timegreater than 10 days [EPRI, 1990]. In general, these include projects with watersheds

yielding moderate to heavy amounts of organic sediments and located in a climate wherethermal stratification isolates bottom water from oxygen-rich surface water. At the sametime, organisms and substances in the water and sediments consume and lower the DO inthe bottom layer. For projects with bottom intakes, this low DO water may createproblems both within and downstream from the reservoir, including possible damage toaquatic habitat.

Before about 1980, detailed studies of the potential impacts of hydropower on waterquality, including low DO, generally were not required prior to licensing. In 1986,however, the Electric Consumers Protection Act (ECPA) defined a process by which thedevelopment of hydropower must be balanced with concerns for the protection ofenvironmental site characteristics. As a result of ECPA, and based on criteria developedby the U.S. Environmental Protection Agency, requirements for monitoring andmaintaining DO levels have become a regular part of license agreements for affectedhydro projects. Among the largest owners of affected hydro projects, however, arefederal agencies, which are exempt from the licensing protocol of the Federal EnergyRegulatory Commission (FERC). These include the U. S. Bureau of Reclamation(USBR), the U. S. Army Corps of Engineers (USACE), and the Tennessee ValleyAuthority (TVA).

Development of Technologies for DO Enhancement

Under the self-imposed targets and deadlines of a five year, $50,000,000 LakeImprovement Program funded from power system revenues, TVA developed a variety ofnew technologies for increasing DO in turbine discharges and successfully resolvedminimum flow and dissolved oxygen problems throughout its reservoir system. Theminimum flow and water quality enhancements have been responsible for the recovery of290 km of aquatic habitat lost due to intermittent drying of the riverbed and for DOimprovements in more than 480 km of rivers below TVA dams [March and Fisher, 1999].The technologies developed and deployed under the Lake Improvement Plan includeminimum flow hydropower units, reliable line diffusers for cost-effective oxygenation ofreservoirs upstream from hydro plants, effective labyrinth weirs and infuser weirs whichprovide minimum flows and aerated flows downstream from hydro plants, retrofit turbineaeration systems, and aerating turbines. Aerating turbines, which use the low pressurescreated by flows through the turbines to induce additional air flows, are typically themost cost-effective DO enhancement technology for the Francis-type turbines typical ofhydroplants with DO concerns. This report focuses on aerating turbine technologies fornew turbine installations and turbine upgrades.

Historical Perspective on Aerating Turbines

In the 1950s, turbine venting was introduced in Wisconsin to reduce the water qualityimpact of discharges from the pulp and paper industry and from municipal sewagesystems [Lueders, 1956]. Research was also conducted in Europe to develop turbinedesigns that would boost dissolved oxygen (DO) levels in water passing through lowhead turbines [Wagner, 1958]. By 1961, turbine aeration systems were operating in theU. S. at eighteen hydroplants on the Flambeau, Lower Fox, and Wisconsin Rivers [Wileyet al., 1962; Wisniewski, 1965].

Aeration systems using draft tube deflectors were developed using physical model testsand installed by Alabama Power during the 1970s at ten turbines in hydroplants on theBlack Warrior and Coosa Rivers, resulting in DO increases of 0.5 to 1.0 mg/L andefficiency losses up to 2% [Bohac et al., 1983]. During the late 1970s and early 1980s,the Tennessee Valley Authority (TVA) developed small, streamlined baffles, called hubbaffles, which reduced energy losses while increasing air flows and operating range. Thehub baffles installed at TVA’s Norris Project provided DO uptakes averaging 2 to 3 mg/Lwith typical efficiency losses of 1 to 2% [Bohac et al., 1983].

During the mid-1980s, Voith Hydro Inc. and TVA invested in a joint research partnershipto develop improved hydro turbine designs for enhancing DO concentrations in releasesfrom Francis-type turbines. Scale models, numerical models, and full-scale field testswere used in an extensive effort to validate aeration concepts and quantify keyparameters affecting aeration performance. Specially-shaped geometries for turbinecomponents were developed and refined to enhance low pressures at appropriatelocations, allowing air to be drawn into an efficiently absorbed bubble cloud as a naturalconsequence of the design and minimizing power losses due to the aeration. TVA’sNorris Project, which was scheduled for unit upgrades, was selected as the first site todemonstrate these “auto-venting” or “self-aerating” turbine technologies. The two Norrisaerating units contain options to aerate the flow through central, distributed, andperipheral air outlets, as shown in Figure 1-1.

In testing the aerating turbines, measurements were required to evaluate both thehydraulic and the environmental performance of the aeration options. The hydraulicperformance is based on the performance compared to the original turbines and theamount of aeration-induced efficiency loss. The environmental performance is evaluatedprimarily by the amount air flow and the amount of the DO uptake. At Norris, eachaeration option was then tested in single and combined operation over a wide range ofturbine flow conditions.

Compared to the original Norris turbines, the innovative aerating replacement unitsprovide overall efficiency and capacity improvements, weighted over the operating range,of 3.7 percent and 10 percent, respectively, as shown in Figure 1-2 [March and Fisher,1999]. This corresponds to an additional annual generation, for the same amount ofrainfall, of about 17,000 MWh for the Norris Project. The new turbines have also shownsignificant reductions in both cavitation and vibration.

For environmental performance, results show that up to 5.5 mg/L of additional DOuptake can be obtained for single unit operation, with all aeration options operating and azero level of incoming DO. In this case, the amount of air induced into the turbine ismore than twice that obtained in the original turbines, which had a retrofitted aerationsystem utilizing hub baffles. At the Norris Project, turbine aeration is typically initiatedin July, when the DO level monitored upstream from the turbines begins to drop.Throughout the low DO season, various combinations of aeration options are used, basedon the head, power, and required DO uptake. Aeration typically ends in November, whencold, dense surface water promotes enough vertical mixing to reduce the thermalstratification. Typical DO improvement through the Norris turbines is 5.5 mg/L, with anadditional 0.5 mg/L of DO improvement obtained from air entrainment in the flow over a

Figure 1-1Sectional View of Norris Francis Turbine Showing Distributed Aeration (Green), Central

Shaft Aeration (Blue), Central Vacuum Breaker Aeration (Red),and Peripheral Aeration (Yellow)

Figure 1-2Hydraulic Performance Results for Norris Aerating Francis Turbine

Distributed Air

water water

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Norris Unit 2 Acceptance TestsComparison of Pre-Mod & Post-Mod Efficiency Tests

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Pre-Mod Test Point Feb. 1995

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Figure 8.5

Corrected to 160 ft Net Head

Norris Unit 2 Acceptance TestsComparison of Pre-Mod & Post-Mod Efficiency Tests

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Unit 1 Pre-Mod Test Point Feb. 1995

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Figure 8.5

Corrected to 160 ft Net Head

re-regulating weir that provides minimum flows downstream from the powerhouse tomeet the DO target level of 6.0 mg/L. Results from bioenergetics modeling of troutgrowth, calibrated and confirmed by fishery studies, indicate a 270% increase in theannual growth for a downstream DO of 6 mg/L compared to the base case withoutenvironmental improvements and a 160% increase in the annual growth compared to theprevious Norris hub-baffle aeration system that maintained a downstream DO ofapproximately 4 mg/L.

As shown in Figure 1-3, typical efficiency losses during aeration at Norris range from -0.2 to +4 percent, depending on the operating conditions and the aeration option oroptions used. For the Norris aerating turbines, the central aeration option has the highestimpact on efficiency, the peripheral aeration option has an intermediate impact onefficiency, and the distributed aeration option has the least impact on efficiency. Theaverage aeration-related turbine efficiency loss during the July to November aerationperiod has been held to less than 2 percent at the Norris Project.

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Figure 1-3Typical Effects of Aeration on Hydraulic Performance for Norris Francis Turbine

The successful demonstration of multiple technologies for turbine aeration at TVA’sNorris Project in 1995 has helped to develop market acceptance for aerating turbines.Major turbine manufacturers who currently offer aerating turbines include ALSTOM,American Hydro, Andritz, and Voith Hydro.

2. UPDATED LITERATURE REVIEW

Review of Recent Literature (1998 - 2009)

In the past, several comprehensive reviews, covering a wide range of techniques andtechnologies for improving the dissolved oxygen (DO) levels in releases fromhydroelectric projects, were completed [Bohac et al., 1983; EPRI, 1990]. Most recently,EPRI [2002] discusses hydrological conditions contributing to low DO levels inreservoirs, describes biological effects of low DO levels, provides a comprehensivesummary of techniques and technologies for improving low DO levels, and discusses DOmodeling and monitoring. EPRI [2002] also includes case studies for the aeratingturbines at TVA’s Norris Project and the “second-generation” aerating turbines at Duke’sWateree Project.

The current paper and the related report [March, 2009] supplement EPRI [2002] byfocusing primarily on aerating turbine technologies for new turbine installations andturbine upgrades. The literature review in the following portions of Section 2 describesaerating turbine technologies reported during the period from 1998 through 2009. Thisdate range provides several years of overlap with EPRI [2002] and updates some of theEPRI [2002] references.

Overview Papers

During the 1998 - 2009 period for this review, several papers provide an overview ofDO-related topics.

March and Fisher [1999] discusses technologies for turbine design and control systems toimprove dissolved oxygen levels in turbine discharges and survival of fish during turbinepassage. The paper describes development, testing, and test results for thesetechnologies, with an emphasis on collaboration of stakeholders and balance betweenenvironmental stewardship and economical power production.

Čada et al. [1999a] and Čada et al. [1999b] describe the U. S. Department of Energy’s Advanced Hydropower Turbine System Program and its goal of maximizing hydropowerresources while minimizing adverse environmental effects. In addition to discussing fishpassage issues, these papers provide a summary of DO concerns, low DO mitigationtechnologies, and aerating turbine progress.

Black et al. [2002] summarizes technological advances achieved between 1990 [EPRI,1990] and 2002 [EPRI, 2002]. The paper includes results from a review of FERCdocuments related to low DO levels for approximately 300 projects. Over one-third ofthe licenses reviewed include requirements for the applicants to maintain a minimum DOlevel in the tailrace. The paper provides a matrix comparing technologies for mitigationof low DO levels and commenting on their general advantages and disadvantages. Foraerating turbines, the listed advantages include a broad operational range, high levels ofDO uptake, reduced efficiency losses compared to baffles or other air injection methods,reduced O&M costs, and minimum efficiency impact during non-aerating operations.The listed disadvantage is a high initial cost, which can be reduced by incorporatingaeration capabilities into a scheduled turbine rehabilitation.

Retrofitted Turbine Aeration Systems

During the 1998 - 2009 period for this review, a variety of papers describe retrofittedturbine aeration systems. Retrofitted turbine aeration systems, typically using theexisting vacuum breaker system, additional air piping through the headcover, and/or drafttube ports below the turbine, are one of the least expensive forms of aeration in terms ofinitial cost. However, life-cycle costs can be substantial due to efficiency losses andincreased O&M costs.

Jarvis et al. [1998] describes early work with turbine venting at Ameren Missouri’sOsage Project in central Missouri.

Harshbarger et al. [1999] provides a summary of results for retrofitted turbine aerationssystems at the U. S. Army Corps of Engineers’ eight-unit, 340 MW Bull Shoals Project,the two-unit, 80 MW Norfork Project, and the four-unit, 200 MW Table Rock Project.The retrofitted turbine aerations systems increased air flows and resulted in typical DOuptakes of 1 to 2 mg/L at Bull Shoals for eight-unit operation, 2 to 2.5 mg/L at Norforkfor two-unit operation, and 2 to 3 mg/L at Table Rock for single unit operation. Littleimpact on efficiency or capacity was observed for Bull Shoals and Table Rock. AtNorfork, the overall efficiency and capacity were relatively unchanged, but the bestefficiency point shifted from 38 MW to 33 MW and the efficiency at maximum capacitydropped by about 2%, both of which have implications for optimized plant operations.

Shultz et al. [2002] reports the successful use of unsteady flow and water quality modelsto evaluate operating scenarios included DO improvements from the retrofitted draft tubeaeration system installed at the PPL Holtwood LLC’s 40 MW Lake WallenpaupackProject.

Ware et al. [2004] discusses American Hydro’s Retrofit Aeration System (RAS), which isa design methodology utilizing computational fluid dynamics (CFD) analyses,mechanical redesign of air and water passageways, and procedures for implementing theRAS with minimal outage time. The RAS methodology was applied at AmerenMissouri’s Osage Project to Unit 3, an aerating replacement turbine supplied byAmerican Hydro in 2002, and to Unit 6, an original Osage turbine supplied by Allis-Chalmers in the early 1930s. For Unit 3, DO uptakes ranged from 4 mg/L at low flows to2.5mg/L at high flows. The corresponding Unit 3 efficiency losses ranged from -40%(i.e., an efficiency improvement) at low flows to 4% at high flows. For Unit 6, DOuptakes ranged from 3.5 mg/L at low flows to 0.4 mg/L at high flows. Thecorresponding Unit 3 efficiency losses ranged from -20% (i.e., an efficiencyimprovement) at low flows to 0% at high flows. The authors conclude that “…a refinedturbine upgrade, including re-runnering, will provide the best environmentalenhancement, and yet very significant improvements to water quality can be made byimplementing a Retrofit Aeration System to existing turbine hardware.” Information onsubsequent retrofit modifications to Osage Unit 6, including additional air piping and adraft tube door vent, is provided in Ware and Sullivan [2006].

Désy et al. [2004] describes the collaboration between the U. S. Bureau of Reclamation(USBR) and G. E. Hydro (now Andritz) to evaluate alternative aeration solutions and,ultimately, to choose a retrofitted peripheral aeration system for the USBR’s Canyon

Ferry Project. Canyon Ferry includes three 18 MW Francis units. DO uptakes rangingfrom 5.6 mg/L at low loads to 2.1 mg/L at maximum load were predicted.

Moore [2009] provides information on the retrofitted draft tube aeration systems installedon three units at Southern Company’s 18 MW Lloyd Shoals Project, located in Georgiaon the Ocmulgee River. These systems allowed the project to meet Georgia’s DOrequirement (i.e., a minimum discharge DO of 4 mg/L and an average of 5mg/L) withoutusing the downstream aerating weir, which needed costly repairs. During aeration,additional efficiency losses of 2 to 3% are experienced at Lloyd Shoals.

Aerating Turbines

During the 1998 - 2009 period for this review, a variety of papers describe aeratingturbines. Aerating turbines are designed to use the low pressures created by flowsthrough the turbines to induce additional air flows.

Jablonski and Kirejczyk [1998] provides some information on the new, centrally aeratingALSTOM turbines installed at Unit 1 of Duke Power Company’s two-unit, 36 MWOxford Project and at Unit 3 of Duke’s four-unit, 60 MW Wylie Project. Duke evaluatedlow DO mitigation technologies, including vacuum breaker venting, forebay oxygendiffusers, retrofitted turbine venting, and forced air venting on the basis of capital costs,maintenance costs, lost capacity due to aeration, and lost efficiency due to aeration.Because Duke was also preparing specifications for replacement turbines for Oxford andWylie under their Upgrade and Modernization Program, the selection of new aeratingturbines was a cost-effective solution. Capital costs for the aeration systems were lessthan 8% of the total turbine costs, with no additional efficiency losses or capacity losseswhen the aeration systems are not in operation.

ALSTOM’s central aeration system channels air to the runner cone from an air intakelocated in the head cover. Performance test results for Oxford and Wylie showed that airflow can have a significant impact on loss of capacity and efficiency. For example,efficiency losses up to 2.5% at maximum gate opening and 9.6% in the vicinity of thebest efficiency gate opening were experienced. Station operators use guide charts tocontrol air valve settings based on wicket gate opening, tailwater elevation, and DOtarget levels and to provide the proper balance between power production and DOenhancement. Gaffney et al. [1999] summarizes Jablonski and Kirejczyk [1998] andprovides additional information on Duke’s Upgrade and Modernization Program.

Papillon et al. [2000a] and Papillon et al. [2000b] describe an ALSTOM central aerationsystem and provide rules of similitude for interpreting and scaling results from physicalmodel test of the aeration systems. Results from model tests and prototype tests arepresented as confirmation. Papillon et al. [2002] provides model test results for threevariations of ALSTOM’s central aeration system and a peripheral aeration system. Theperipheral aeration system had a significantly lower impact on efficiency compared to thecentral aeration alternatives.

Sigmon et al. [2000] discusses the evaluation of four DO enhancement methods forDuke’s Wateree Project, including vacuum breaker aeration, retrofitted central aeration,an aerating replacement turbine, and a forebay oxygen injection system. The alternative

selected for Wateree Unit 3 was a Voith Hydro replacement turbine with distributedaeration, due to the long term environmental benefits from increased DO uptake and theoperational flexibility for increased generation during the time of year when DO is lowand energy values are high. Reported DO uptakes range from a low of 3.9 mg/L to a highof 4.3 mg/L as output power ranges from 9 MW to 19 MW.

Parrott and Fisher [2003] provides preliminary results from the installation of Unit 5, thefirst upgraded unit at the USACE’s seven-unit, 364 MW Thurmond Project with a VoithHydro distributed aeration system. The distributed aeration system draws air from threeair intakes located in the head cover through hollow turbine blades to the trailing edge ofeach blade. Additional information is provided in Parrott and Fisher [2006] and Hobbs[2008] (see below).

Fraser et al. [2005] describes the use of physical model tests to measure and predict theeffects of central and peripheral air injection on the DO levels and operating efficienciesfor a GE (now Andritz) Francis turbine. The paper also includes some discussion ofsimilitude requirements for predicting prototype aeration performance from a physicalmodel study.

Kepler and Hager [2005] and Hager [2006] describe the runner upgrade for Unit 5 atExelon Power’s 514 MW Conowingo Hydroelectric Generating Station, located on theSusquehanna River. The upgraded runner was designed for low flow operationalcapability, increased efficiency, increased capacity, and DO enhancement. VoithHydro’s distributed aeration system channels air from six air intakes located in the headcover through hollow turbine blades to the trailing edge of each blade. Each air intakeincludes a valve operated by the control system. Performance results were not availableat the time of publication.

Parrott and Fisher [2006] updates results for the USACE’s Thurmond Project as moreunits have been upgraded with distributed aeration Voith Hydro turbines. Additional DOuptakes up to 4 mg/L are reported, as well as significant water quality improvementsthroughout a monitored 16-mile reach of the Savannah River downstream from theThurmond Project.

Hobbs [2008] describes the USACE Savannah District’s experience with three DOenhancement technologies, including a retrofitted turbine aeration system at the five-unit,432 MW Hartwell Project, a forebay oxygen diffuser system at the eight-unit, 684 MWRussell Project, and distributed turbine aeration at the seven-unit, 364 MW ThurmondProject. The retrofitted turbine aeration system at Hartwell provides DO uptakes up to 3mg/L with a corresponding efficiency loss of 0.5%. The Voith Hydro distributed aerationsystems for all of the Thurmond turbines draw air from three air intakes located in thehead cover of each unit through hollow turbine blades to the trailing edge of each blade.The turbine efficiency impact is 0.2% when providing 2 mg/L of DO uptake, and theturbines are capable of providing more than 4 mg/L. This paper also describes severaladvanced control and monitoring systems for turbine efficiency, water quality, oxygendiffuser control, and turbine aeration control.

Foust et al. [2008] provides some of the most comprehensive results for central,peripheral, and distributed aeration systems. The paper presents data on the relationships

among aeration airflows, aeration injection locations, and aeration system head losses anddiscusses the effects of air induction on local pressures. For flow rates approximately20% below best efficiency, central aeration provides the largest pressure differentials andair induction capability, followed by distributed aeration and peripheral aeration. Forflow rates from 10% below best efficiency to maximum capacity, distributed aerationprovides the largest pressure differentials. The effect of aeration on local pressures isgreatest for central aeration, followed by peripheral aeration. Distributed aeration has theleast effect on local pressures. Consequently, when local pressures are adjusted for theeffects of aeration, distributed aeration shows the potential for inducing the largest airflows into the turbine. The paper also examines the influence of aeration technology onturbine performance. For flow rates approximately 20% below best efficiency, peripheralaeration and distributed aeration provide the lowest impact on turbine efficiency, andcentral aeration provides the highest impact, up to 13% for air/water flow ratios of 5%.For flow rates at best efficiency, peripheral aeration and distributed aeration provide thelowest impact on turbine efficiency, and central aeration provides the highest impact, upto 17% for air/water flow ratios of 5%. For flow rates at 20% above best efficiency,peripheral aeration and distributed aeration provide the lowest impact on turbineefficiency, and central aeration provides the highest impact, up to 25% for air/water flowratios of 5%. In addition, for flow rates from best efficiency to 20% above bestefficiency, distributed aeration is significantly more efficient than peripheral aeration.Field data is also presented to show that the DO uptake efficiency for distributed aerationis significantly greater than the DO uptake efficiency for central aeration and peripheralaeration. At best efficiency, the DO uptake efficiencies are 42%, 33%, and 23% fordistributed aeration, peripheral aeration, and central aeration, respectively.Corresponding results at flows of 20% above best efficiency, typical of maximum load,show DO uptake efficiencies of 54%, 38%, and 36% for distributed aeration, peripheralaeration, and central aeration. The authors conclude that the highest DO uptakes and thelowest impacts on efficiency are achieved with a distributed aeration system, followed bya peripheral system.

Rohland and Sigmon [2008] describe a Voith Hydro aeration system designed for areplacement powerhouse at the Bridgewater Hydroelectric Station near Nebo, NorthCarolina. While distributed aeration would have been the preferred solution, the smallsize of the runner required the substitution of a combined system using both centralaeration and peripheral aeration. Both central and peripheral aeration will be used duringperiods of low flow operation, and only the peripheral aeration will be used duringperiods of high flow operation requiring DO enhancement.

Foust et al. [2009] describes airflows, efficiency effects, and oxygen uptakes associatedwith new distributed aeration turbines installed at Ameren Missouri’s OsageHydroelectric Project on the Osage River near Lake Osage, Missouri. This eight-unit,240 MW plant has recently installed four new Voith Hydro turbines with distributedaeration and has conducted extensive hydraulic and environmental performance tests onthe units. Air/water flow ratios ranged from 3.2% to 6.6%, depending on flow rate andtailwater elevation. At best efficiency flows, impacts on turbine efficiency ranged from1.6% at an air/water flow ratio of 4.8% to 3.5% at an air/water flow ratio of 6.4%. Atflows 10% above best efficiency, impacts on turbine efficiency ranged from 2.1% at an

air/water flow ratio of 4.5% to 4.1% at an air/water flow ratio of 6.0%. During theperformance testing, typical incoming DO levels ranged from 2.1 mg/L to 2.4 mg/L, andtypical outflow DO levels ranged from 5.7 mg/L to 6.3 mg/L, depending on tailwaterlevel and flow. At the lowest tailwater level, DO uptakes ranged from 4.4 mg/L to 5.1mg/L, and at the highest tailwater level, DO uptakes ranged from 3.4 mg/L to 3.8 mg/L.At all of the tested tailwater levels, the effect of aeration on turbine efficiency was lessthan 1% for DO uptakes up to 3 mg/L.

Kao [1997], Kao et al. [1998], and Kao et al. [1999] describe an innovative turbinedesign which includes an updraft flow arrangement, a vertical flow control valvereplacing the wicket gates, a divergent flow chamber replacing the draft tube, and exitflow into the tailwater free surface. Laboratory results show that this design may provideeffective tailwater aeration.

Related Topics

During the 1998 to 2009 period for this review, several papers describe topics related toaerating turbines.

For example, Almquist et al. [1998] provides a draft test code for evaluating theperformance of aerating turbines. This draft test code is also included as an appendix to afinal report under the U. S. Department of Energy’s Advanced Hydropower TurbineSystem Program [Franke et al., 1997].

Hopping et al. [1999] reports “lessons learned” from the Norris experience with multipleaeration technologies. The paper provides industry guidelines on economic justificationfor turbine aeration systems, preparation of appropriate procurement specifications forturbine aeration systems, and verification of the hydraulic and environmentalperformance of turbine aeration systems.

Faulkner [2000] describes applications for environmental monitoring at hydroplants,including DO and other water quality monitoring. The article provides information onthe environmental monitoring and optimization system used by TVA for the aeratingturbines at the Norris Project.

Peterson et al. [2001] addresses multiple approaches to DO improvements at hydropowerfacilities. These include structural approaches (e.g., aerating turbines, aerating weirs,oxygen diffuser systems), operational approaches (e.g., modified timing and duration offlow releases), and regulatory approaches (e.g., site-specific DO standards, standardsbased on biocriteria, watershed-based trading). The authors conclude, “A combination ofmitigation techniques, including structural, operational, and regulatory approaches, maybe the most effective way to address DO problems at hydropower projects.”

Kühlert and Ware [2004] discusses the development of a computational fluid dynamics(CFD) model to understand and predict performance of retrofitted aeration systems forAmeren Missouri’s Osage Project. The model was used to analyze effects on turbineperformance, pressure losses in air flow passageways, air flow rates, and DO uptake forpotential design modifications to the retrofitted aeration system.

Bevelheimer and Coutant [2006] describes a modeling study to predict downstreamenvironmental benefits which can be achieved due to low DO mitigation techniques, suchas aerating turbines. A suite of models simulated hydrodynamics, water quality, and fishgrowth as affected by DO, water temperature, and food availability for a 26-mile portionof the Caney Fork River downstream from Center Hill Dam. The study assessed theeffects of alternative mitigation techniques and levels of improvement on the waterquality and fish growth throughout the modeled portion of the river. The authors notethat results from the study demonstrate the value of the modeling techniques forevaluating tradeoffs among hydropower operations, power generation, and environmentalquality.

March [2006] discusses modern systems for plant optimization, unit commitment, andcontrol that combine environmental constraints associated with increased dissolvedoxygen levels, the effects of the environmental operations on unit performance, andperiodic optimization at the system level and the plant level, including real-time plantoptimization for the constantly varying loads associated with automatic generationcontrol (AGC). The paper provides several examples, including aerating turbines at theUSACE’s Thurmond Project and Ameren Missouri’s Osage Project, to show that periodicand real-time environmental optimization can lead to improved environmentalperformance, improved operating efficiencies, and improved profitability. Smith et al.[2007] extends the discussion of environmental optimization to include the challenges ofselecting environmental objectives considering ecosystem complexity and the differinguncertainty, time scales, and hierarchy between conventional hydro system optimizationand emerging concepts of environmental optimization.

McGinnis and Ruane [2007] describes the development of a discrete-bubble model(DBM) for two hydropower projects, Duke’s Wylie Project and South Carolina Electric& Gas Company’s Saluda Project. The DBM predicts the rate of oxygen transfer from asingle bubble traveling through a draft tube and tailrace as a function of flow rate,air/water ratio, and bubble size. The model was used successfully to predict thedischarge DO for the Saluda Project and the Wylie Project to within 10% of the observedvalues. Ruane and McGinnis [2007] details the application of the discrete-bubble modelat the Saluda Project for a variety of operating policy scenarios, resulting in a cost-effective, site-specific DO standard for the Lower Saluda River.

3. HYDRAULIC AND ENVIRONMENTAL PERFORMANCE

Introductory Remarks

Performance testing is typically conducted to verify conformance with environmental andhydraulic goals or guarantees for aerating turbines [Hopping et al., 1999]. As shown inFigure 3-1, testing of aerating turbines can be broadly divided into two categories,aeration and non-aeration performance testing. Non-aeration testing is conducted with allaeration systems off, and essentially identical to the performance testing of conventionalhydroturbines. Typical parameters include turbine efficiency, maximum power,cavitation level, vibration, shaft runout, and thrust load. Testing of an aerating turbineencompasses additional evaluations for both environmental performance and hydraulic

performance. Environmental performance is typically measured by the DO uptake andsometimes the level of total dissolved gases (TDG). Air flow is needed to verify gastransfer characteristics of individual aeration options. The hydraulic performance ismeasured by the aeration-induced efficiency change, . In computing both a (withaeration) and 0 (without aeration) are found using the procedures of PTC-18 or IEC 41.Airflow and pressures at the aeration outlets are desirable to verify hydrauliccharacteristics of individual aeration options. Aeration can affect other mechanicalaspects of turbine operation, so measurements for cavitation and vibration can also be apart of aeration performance testing.

To help the hydro industry standardize the proper procedures by which DO, η, and other parameters should be measured and evaluated, TVA engineers used the Norrisaerating turbine testing as the bases for developing a draft test code for aerating turbines[Almquist et al., 1998]. The draft test code gives guiding principles for determining theenvironmental and hydraulic performance of aerating turbines. Included arerecommendations for methods of measurement, instrumentation, test procedures, andanalysis of data. The draft test code is also included in a final USDOE Advanced HydroTurbine Project report [Franke et al., 1997].

Hydraulic Performance

For this paper, the terminology in Figure 3-1 is simplified. Environmental performanceis unchanged, but hydraulic performance combines mechanical performance andhydraulic performance from Figure 3-1. Test codes, such as PTC-18 [ASME, 2002] andIEC 41-1991 [IEC, 1991], apply and include procedures to measure flow rate, head, andpower output to calculate the turbine efficiency. Because changes in performance, ratherthan absolute performance, are of primary interest, index testing is often utilized foraeration performance tests.

Figure 3-1Flowchart for Testing Aerating Hydroturbines, from Hopping et al. [1999]

Performance Testing of Aerating Hydroturbines

Turbine efficiencyMaximum power outputCavitation levelsVibrationShaft runoutThrust load

Non-Aeration Performance


Aeration Performance

Environmental Performance

Aeration-induced efficiency changeAirflowPressure at aeration outlets

Mechanical Performance

DO uptake DO)Total dissolved gas (TDG)Other water quality parametersAirflow


Difficulties in evaluating environmental performance are graphically illustrated in Figure3-2. Errors in the measurement of dissolved oxygen contribute significant to theuncertainty associated with determining the environmental performance (i.e., DO uptake)[Hopping et al., 1999]. This is primarily due to spatial variations of DO in the turbinepenstock and in the tailwater. Variations in the penstock result from DO stratification inthe reservoir and withdrawal flow patterns, while variations in the tailwater are due toincomplete mixing of air in the turbine discharge and an uneven distribution of flow inthe tailrace.

Figure 3-2Sectional Diagram Illustrating Difficulties in Testing Aerating Hydroturbines

Due to these variations, the estimated confidence interval for measured values of DO caneasily vary between 0.5 mg/L and 1.0 mg/L, which can creates large uncertainty in thecomputed DO uptake. The effect of large uncertainty in DO uptake can be costly, notonly in determining conformance to environmental performance guarantees, but also interms of supplying and operating DO enhancement systems. With a large uncertainty, aconservative approach must be taken in selecting and operating these environmentalsystems.

To increase accuracy in the measurement of turbine environmental performance, the drafttest code for aerating turbines recommends multiple DO readings in the turbine penstockand tailwater. Uncertainty in the incoming DO can be reduced by obtaining independent,continuous DO measurements from multiple taps upstream from the turbine. In thetailwater, multiple, continuous DO measurements at several points across the turbinedischarge are recommended. The optimum number of tailwater sensors depends on themagnitude of DO spatial variations and the size of the tailrace. Due to the high cost ofdeploying multiple sensors, it is beneficial to perform a pre-test evaluation of velocityand DO patterns in the tailrace. This will allow DO sensors to be strategically located toavoid redundant measurements in areas of flow stagnation or recirculation. Pre-test, mid-

test, and post-test calibrations of DO sensors in a common bath to a common standardalso should be performed to reduce uncertainty.

4. CASE STUDIES

Overview

The three case studies in this section describe examples where utilities have, to varyingdegrees, assessed the hydraulic and environmental performance of aerating turbinetechnologies and provided results for incorporation into this paper. The case studiesdescribe the available hydraulic and environmental performance information for aeratingturbines using peripheral, central, and distributed aeration.

Case Study, Aerating Turbine with Peripheral Aeration

Description of Plant

This four-unit, 119 MW hydroplant is owned and operated by an industrial utility. In2001, Unit 4 was upgraded with a Voith Hydro Inc. aerating turbine using peripheralaeration supplied through two air inlets. This case study is based on results for Unit 4.Subsequently, two additional units at this plant have been upgraded with similar aeratingturbines using peripheral aeration.

In preparation for turbine upgrades and modernization, index tests were conducted onUnit 4 in 1999. After the Unit 4 runner upgrade in 2001, additional index tests wereconducted to evaluate the new unit. Air flows into the peripheral aeration system werealso measured, using differential pressures measured at the throats of the bellmouthintakes for the air supply piping. For the Unit 4 upgrade, a complete physical modelstudy, including the draft tube, was conducted. The best efficiency results from themodel study were used as the index reference for the test results reported in this casestudy.


Physical model test results and index test results for Unit 4 are shown in Figure 4-1. Thepeak efficiency from the physical model results has been used to “index” and normalizeboth the upgraded turbine results and the original turbine results. The shape of theefficiency curve for the prototype turbine agrees closely with the model results. Withoutaeration, the upgraded turbine achieves a best efficiency increase of about 2% and acapacity increase of 4 MW, about 14%, compared to the original turbine. Withmaximum aeration, the upgraded turbine achieves a best efficiency increase of about 1%and a capacity increase of 2.7 MW, about 9.5%, compared to the original turbine. Withmaximum aeration, the best efficiency point remains at 24 MW, similar to the originalunit. With no aeration, the best efficiency point is at 27 MW. Actual efficiency lossesduring operation are lower than these values when DO and TDG targets can be met withreduced air flows.

Index Test Results (Peripheral Aeration)Net Head = 174.5 ft

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Original Unit, No Aeration

Figure 4-1Hydraulic Performance for Aerating Turbine with Peripheral Aeration (Net Head 174.5 ft)


Only limited environmental performance data is available for this unit. Figure 4-2 showsair flow results as the percentage ratio of volumetric air flow to volumetric water flow,Qa/Qw, also called φ, versus turbine output expressed in megawatts (MW). Qa/Qw valuesbetween 8% and 9% are achieved in the range of 10 MW to 17 MW. When the vacuumbreaker closes above 17 MW, the Qa/Qw value drops to 7%. At 22 MW, the Qa/Qw valuesbegin to drop gradually throughout the remaining power range, with a low of 5% at themaximum load of 31 MW. Based on previous experience with other installations, thesevalues of Qa/Qw should be able to provide DO uptakes of about 4 mg/L to 6 mg/L.

Additional Information

Additional, more comprehensive information on environmental performance could beobtained from this site through detailed analyses of plant operational data andenvironmental monitoring data.

Qa/Qw Versus Turbine Output (Peripheral Aeration)Net Head = 174.5 ft

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Figure 4-2Qa/Qw Versus Turbine Output for Aerating Turbine with Peripheral Aeration

(Net Head 174.5 ft)

Case Study, Aerating Turbine with Central Aeration


This eight-unit, 240 MW hydroplant is owned and operated by an investor-owned utility.In 2002, Units 3 and 5 were upgraded with aerating turbines using central aeration,supplied by American Hydro Company. The original units, supplied by Allis-Chalmers,were also retrofitted with central aeration. This case study is based on test results forUnit 3.

In preparation for additional turbine upgrades and modernization, efficiency tests wereconducted on Unit 3 and Unit 6 in 2005. Efficiency test procedures followed ASMEPerformance Test Code 18-2002 [ASME, 2002]. The pressure-time method was used forwater flow measurements. Air flows into the central aeration systems were alsomeasured, using differential pressures measured at the throats of the bellmouth intakesfor the air supply piping.

The plant’s original design also included two small station service units, manufactured byAllis-Chalmers. Each of the station service units was designed to operate at 170 cfs andapproximately 60% efficiency. The station service units were replaced in 2010 withAmerican Hydro units including peripheral aeration, rated for 3.6 MW and 450 cfs at 90ft of head and operating at approximately 90% efficiency.


Numerical model predictions for Unit 3 performance and results from the 2005 efficiencytests for Unit 3 and Unit 6 are shown in Figure 4-3. The peak efficiency from thenumerical model results has been used to normalize both the upgraded Unit 3 turbineresults and the original Unit 6 turbine results. Without aeration, the upgraded Unit 3turbine achieves approximately equal efficiency and a capacity increase of 6.3 MW,about 21%, compared to the Unit 6 original turbine. With maximum aeration, theupgraded turbine achieves approximately equal efficiency at maximum capacity and acapacity increase of 3.2 MW, about 11%, compared to the Unit 6 original turbine. Actualefficiency losses during operation are lower than these values when DO and TDG targetscan be met with reduced air flows.

Net Head Efficiency Test Results (Central Aeration)Net Head = 95 ft

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Numerical Model Prediction

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2002 Upgraded Unit, Central Aeration On (Qa/Qw = 2.7% to 4.4%)

Original Unit, Central Aeration Off

Original Unit, Central Aeration On (Qa/Qw = 0% to 3.1%)

Figure 4-3Hydraulic Performance for Aerating Turbine with Central Aeration (Net Head 95 ft)


Figure 4-4 shows air flow results as Qa/Qw versus turbine output expressed in megawatts(MW). Qa/Qw values between 4.4% and 2.7% are achieved in the range of 10 MW to 33MW, with Qa/Qw gradually dropping with increased turbine output. The upgraded Unit 3turbine provides significantly higher Qa/Qw values across the operating range.

Limited DO uptake information, provided for this unit in Ware and Sullivan [2006], isshown for multiple tailwater elevations in Figure 4-5. Incoming DO was measured withinstrumentation installed in the penstock, and tailrace DO was measured from a boat inthe tailrace. The data for a tailwater elevation of 560 ft corresponds to the performance

data reported in this case study. The reported DO uptakes ranged from 4.4 mg/L at aturbine flow of 1,700 cfs to 4.3 mg/L at a turbine flow of 3,900 cfs.

Qa/Qw Versus Turbine Output (Central Aeration)Net Head = 95 ft

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Figure 4-4Qa/Qw versus Turbine Output for Aerating Turbine with Central Aeration (Net Head 95 ft)

DO Uptake Versus Turbine Flow (Central Aeration)

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Tailwater Elevation = 563

Figure 4-5DO Uptake Versus Turbine Flow for Aerating Turbine with Central Aeration,

from Ware and Sullivan [2006]


Additional, more comprehensive information on environmental performance could beobtained from this site through detailed analyses of plant operational data andenvironmental monitoring data.

The project’s new FERC license, issued in 2007, raises the minimum flow from 450 cfsto 900 cfs. The two station service units were upgraded in 2010 to supply the increasedminimum flow as well as 7.2 MW of combined power production. In addition, the newstation service units have aeration capabilities, which can provide increasedenvironmental benefits compared to flow alone [March and Fisher, 1999]. The additionalannual generation benefit from the upgrade to the station service units, certified by FERCfor a production tax credit, is 10,575 MWh [FERC, 2011].

Case Study, Aerating Turbine with Distributed Aeration


This eight-unit, 240 MW hydroplant is owned and operated by an investor-owned utility.In 2008, Units 1 and 7 were upgraded with aerating turbines using distributed aeration,supplied by Voith Hydro Inc. This case study is based on test results for Unit 1.

For the Unit 1 and Unit 7 upgrades, a complete physical model study, including the drafttube, was conducted. After the Unit 1 and Unit 7 upgrades, efficiency tests wereconducted on Unit 3 and Unit 6 in 2008. Efficiency test procedures followed ASMEPerformance Test Code 18-2002 [ASME, 2002]. The pressure-time method was used forwater flow measurements. Air flows into the central aeration systems were alsomeasured, using differential pressures measured at the throats of the bellmouth intakesfor the air supply piping.


Model test results and efficiency test results for Unit 1 are shown in Figure 4-6. The peakefficiency from the physical model results has been used to normalize both the upgradedUnit 1 turbine results and the original Unit 6 turbine results. Within the test uncertainty,the peak efficiency from the model tests corresponds to the measured efficiency. Theshape of the efficiency curve for the prototype turbine agrees closely with the modelresults. Without aeration, the upgraded turbine achieves the best efficiency at turbineoutput of 32.6 MW, which is an efficiency increase of about 3.4% compared to theoriginal turbine, and a maximum capacity of 36.9 MW, which is an increase of 7.4 MW,about 14%, compared to the original turbine. With maximum aeration, the upgradedturbine achieves the best efficiency at a turbine output of 31 MW, which is an efficiencyincrease of about 1% compared to the original turbine, and a maximum capacity of 35.8MW, which is an increase of 6.3 MW, about 21%, compared to the original turbine.With maximum aeration, the efficiency at maximum capacity is 3.8% higher than theefficiency at maximum capacity for the original turbine. Maximum aeration at bestefficiency for Unit 1 reduces the efficiency by 2.4% and reduces the best efficiencyturbine output from 32.6 MW to 31 MW. Actual efficiency losses during operation arelower than these values when DO and TDG targets can be met with reduced air flows.

Net Head Efficiency Test Results (Distributed Aeration)Net Head = 95 ft

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Figure 4-6Hydraulic Performance for Aerating Turbine with Distributed Aeration (Net Head 95 ft)


Figure 4-7 shows air flow results as Qa/Qw versus turbine output expressed in megawatts(MW). Qa/Qw values between 7.4% and 5.0% are achieved in the range of 10 MW to 36MW, with Qa/Qw gradually dropping with increased turbine output between 10 MW and15 MW, leveling off between 15 MW and 26 MW, then rising gradually between 15 MWand 26 MW. The upgraded Unit 1 turbine provides significantly higher Qa/Qw valuesacross the operating range compared to the Unit 6 original turbine.

Limited DO uptake information, provided for this unit in Foust et al. [2009], is shown formultiple tailwater elevations in Figure 4-8. Incoming DO was measured withinstrumentation installed in the penstock, and tailrace DO was measured from a boat inthe tailrace. The data for a tailwater elevation of 562 ft corresponds to the performancedata reported in this case study. The reported DO uptakes ranged from 3.4 mg/L to 3.8mg/L for turbine flows from 3,100 cfs to 4,850 cfs.


Additional information on hydraulic and environmental performance at other heads isprovided in Foust et al. [2009]. More comprehensive information on environmentalperformance could be obtained from this site through detailed analyses of plantoperational data and environmental monitoring data.

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Figure 4-7Qa/Qw Versus Turbine Output for Aerating Turbine with Distributed Aeration

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DO Uptake Versus Turbine Flow (Distributed Aeration)

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Figure 4-8DO Uptake Versus Turbine Flow for Aerating Turbine with Distributed Aeration,

from Foust et al. [2009]

5. DISCUSSION OF RESULTS FROM CASE STUDIES

Aeration Effects on Turbine Efficiency

Typical effects of air flows on turbine efficiency for peripheral, central, and distributedaeration are provided in Foust et al. [2008]. Figures from Foust et al. [2008] are re-plotted and extended to higher values of Qa/Qw (i.e., the volumetric air flow rate dividedby the volumetric water flow rate, expressed as a percentage) in Figures 5-1, 5-2, and 5-3.The original guidelines from Foust et al. [2008] are shown as solid lines, and linearextrapolations are shown as dotted lines. Data points corresponding to test results for thethree case studies are provided in these three figures.

Aeration Influence on Turbine Efficiency (Qw/Qwopt = 0.8)

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Figure 5-1Decreases in Turbine Efficiency for Peripheral (Red), Central (Blue), and Distributed

(Green) Aeration at Qw/Qwopt of 0.8, adapted from Foust et al. [2008]

Figure 5-1 shows typical decreases in turbine efficiency with peripheral aeration (redline), central aeration (blue line), and distributed aeration (green line) for a Qw/Qwopt of0.8 (i.e., a water flow rate which is 80% of the water flow rate at the maximum turbineefficiency without aeration). A Qw/Qwopt of 0.8 corresponds to a flow range that is typicalof the lower limit for a normal operational range. In this flow range, the decrease inefficiency from the peripheral aeration case study is lower than expected, the decrease inefficiency from the central aeration case study is higher than expected, and the decreasein efficiency from the distributed aeration case study is close to the expected value.

Figure 5-2 shows typical decreases in turbine efficiency with peripheral aeration (redline), central aeration (blue line), and distributed aeration (green line) for a Qw/Qwopt of1.0 (i.e., a water flow rate which equal to the water flow rate at the maximum turbineefficiency without aeration). A Qw/Qwopt of 1.0 corresponds to the flow range for the


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most efficient turbine operation. In this flow range, the decrease in efficiency from theperipheral aeration case study is lower than expected, the decrease in efficiency from thecentral aeration case study is somewhat higher than expected, and the decrease inefficiency from the distributed aeration case study is somewhat higher than expected.

Figure 5-2 shows typical decreases in turbine efficiency with peripheral aeration (redline), central aeration (blue line), and distributed aeration (green line) for a Qw/Qwopt of1.2 (i.e., a water flow rate which is 20% higher than the water flow rate at the maximumturbine efficiency without aeration).

A Qw/Qwopt of 1.2 corresponds to a flow range that is typical of the upper limit for anormal operational range. In this flow range, the decrease in efficiency from theperipheral aeration case study is lower than expected, and the decrease in efficiency fromthe distributed aeration case study is close to the expected value. No results are availablefrom the central aeration case study for a Qw/Qwopt of 1.2.

This comparison of the effects of aeration on turbine efficiency from the case studyresults with the typical expected values from Foust et al. [2008] underscores the scatterinherent in the data behind the three lines in each graph. Presumably, site-specific detailssuch as draft tube design contribute significantly to the observed variation.

Efficient Operation and Environmental Optimization

The central aeration case study and the distributed aeration case study describe unitslocated at the same hydroplant. Figure 5-4 shows turbine efficiencies versus turbineoutputs for the three unit types at this plant, operating at a net head of 95 ft. The turbineefficiencies have been normalized to the maximum measured efficiency of the mostefficient unit. The plant has two original units with retrofitted central aeration, two 2002upgraded units with central aeration, and four 2008 upgraded units with distributedaeration. The challenges for efficient operation of the plant’s eight units under non-aerating and aerating conditions, over a range of heads, and with rapid load swings areapparent.

To improve the overall efficiency at this plant, a SCADA (Supervisory Control and DataAcquisition) system upgrade called the “Advanced Features Control System” (AFCS)was implemented. The goal of the AFCS was to optimize overall plant efficiency whileensuring that overriding constraints, such as license compliance and environmentalcompliance, were also met. The AFCS includes unit (i.e., turbine and generator)performance information for non-aerating and aerating operation over the anticipatedhead range of the plant. The control algorithm receives a plant load setting from theIndependent Transmission System Operator (ISO), calculates the optimum method todispatch each of the eight main units, then every few seconds automatically adjusts thepower on each unit to meet the time-varying load setting. As the head changes, theAFCS maintains each operating unit within a narrow band of its most efficient operatingpoint and automatically brings units from condensing operation or reduced load togenerating operation or from generating operation to condensing operation or reducedload as required to meet the total plant load demand.

Net Head Efficiency Test Results (Central and Distributed Aeration)Net Head = 95 ft

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Figure 5-4Normalized Turbine Efficiencies versus Turbine Output for Three Unit Types

For operations under aerating conditions, an Air Order Model (AOM) has beenimplemented to control and optimize the airflows supplied to the eight units. A DiscreteBubble Model (DBM) is incorporated into the AOM. The DBM predicts the rate ofoxygen transfer from a single bubble traveling through the draft tube and tailrace as afunction of flow rate, air/water ratio, and other factors. The DBM, which was calibratedbased on DO uptake tests at the plant, uses real-time data to determine the amount of airthat is needed to attain DO targets in the tailrace. The input data includes inflow DO,unit flow rates, tailrace elevation, temperature, and total dissolved gases (TDG). Usingthe DBM results, the AOM balances airflows among unit, utilizing the most efficientunits first, and controls valves on the air intake piping for each unit to ensure that DO andTDG targets are attained and that excess aeration does not occur. The AOM and DBMself-adjust based on feedback data from the tailrace DO and TDG monitor , which islocated about 1 mile downstream, and the travel time between the powerhouse dischargeand the downstream water quality monitor.

This combination of the Advanced Features Control System and the Air Order Modelprovides an advanced form of environmental optimization that has not been achievedelsewhere. Additional evaluations and improvements to the AFCS and the AOM areongoing.

6. SUMMARY AND RECOMMENDATIONS

Summary

This paper uses a review of the technical literature from 1998 through 2009 and contactswith personnel from turbine manufacturers, utilities, and agencies to provide informationand performance data on aerating turbine technologies. Hydraulic and environmentalperformance results are analyzed and presented as case studies for three aerating turbinetechnologies (central aeration, peripheral aeration, and distributed aeration). The paperdescribes some of the difficulties in assessing the performance of aerating turbines,discusses the implications of the case study results for plant operation and optimization,and provides recommendations for additional related research.

Recommendations

To further assist turbine manufacturers, agencies, and utilities in their efforts to evaluateand improve the hydraulic and environmental performance of aerating turbines, thefollowing recommendations are provided:

Turbine manufacturers, agencies, and utilities should be encouraged to assistthe hydropower industry by providing access to existing hydraulic andenvironmental performance information for aerating turbines.

The hydropower industry should establish a national database of hydraulic andenvironmental performance data for aerating turbines. The national databasecould be funded by EPRI, DOE, USACE, or another appropriate sponsor andmaintained by a national laboratory with related experience, such as OakRidge National Laboratory.

Additional performance information should be solicited for the smaller“minimum flow” turbine installations which include DO enhancement.

Additional performance information should be solicited from European andAsian utilities and agencies as aerating turbine solutions are applied in thoseareas.

ASME PTC-18’s continuing efforts for the development and standardizationof a comprehensive test code for aerating turbines should be encouraged andfinancially supported by the hydropower industry.

Long term monitoring and data analyses for various aerating turbinetechnologies should be conducted to provide hydraulic and environmentalperformance results over a much wider range of conditions.

As a collaborative R&D study and a contribution to the hydropower industry,EPRI should survey turbine manufacturers and utilities and compileincremental cost information for various aerating turbine technologies.

A wide variety of related research activities should be encouraged andsupported. Some of these research topics include:

1. Improving the aeration-related scaling relationships between physicalmodels and prototypes;

2. Improving numerical models for predicting draft tube effects on decreasesin turbine efficiency under non-aerating and aerating conditions;

3. Improving numerical models for predicting gas transfer and resulting DOand TDG levels;

4. Developing cost-effective DO enhancement options for Kaplan and bulbturbine units;

5. Developing and improving environmental optimization tools; and

6. Developing new, more cost-effective methods to measure DO in reservoirreleases.

7. REFERENCES

Almquist, C. W., P. N. Hopping, and P. J. Wolff, “Draft Test Code for AeratingHydroturbines,” TVA Report No. WR98-1-600-125, Norris, Tennessee: TennesseeValley Authority (TVA), August 1998.

ASME, “Performance Test Code 18: Hydraulic Turbines and Pump-Turbines,” ASMEPTC 18-2002, New York, New York: American Society of Mechanical Engineers(ASME), 2002.

Bevelhimer, M. S., and C. C. Coutant, “Assessment of Dissolved Oxygen Mitigation atHydropower Dams Using an Integrated Hydrodynamic/Water Quality/Fish GrowthModel,” Report No. ORNL/TM-2005/188, Oak Ridge, Tennessee: Oak Ridge NationalLaboratory, March 2006.

Black, J. L., E. P. Taft, D. A. Davis, and D. A. Dixon, “Methods for Meeting andMonitoring Dissolved Oxygen Standards for Hydroelectric Projects,” Proceedings ofHydroVision 2002, Kansas City, Missouri: HCI Publications, July 2002.

Bohac, C. E., J. W. Boyd, E. D. Harshbarger, A. R. Lewis, Techniques for Reaeration ofHydropower Releases, USACE Technical Report No. E-83-5, Vicksburg, Mississippi:U. S. Army Corps of Engineers (USACE), February 1983.

Čada, G. F., P. A. Brookshier, J. V. Flynn, B. N. Rinehart, G. L. Sommers, and M. J. Sale, “Advanced, Environmentally Friendly Hydroelectric Turbines for the Restoration ofFish and Water Quality,” Paper IGWM-39, Proceedings of EPRI Conference onIntegrated Global Water Management, September 1999a (cancelled).

Čada, G. F., P. A. Brookshier, J. V. Flynn, B. N. Rinehart, G. L. Sommers, and M. J. Sale, “The use of advanced hydroelectric turbines to improve water quality and fishpopulations,” Proceedings of the 4th International Congress on Energy, Environment, andTechnological Innovation, September 1999b, pp. 545-549.

Désy, N., É. Demers, R. Grenier, and D. O. Hulse, “The Dissolved Oxygen Experience atCanyon Ferry,” Proceedings of HydroVision 2004, Kansas City, Missouri: HCIPublications, July 2004.

EPRI, Assessment and Guide for Meeting Dissolved Oxygen Water Quality Standards forHydroelectric Plant Discharges, Report No. GS-7001, Palo Alto, California: ElectricPower Research Institute (EPRI), November 1990.

EPRI, Maintaining and Monitoring Dissolved Oxygen at Hydroelectric Projects: StatusReport, Report No. 1005194, Palo Alto, California: Electric Power Research Institute(EPRI), May 2002.

Faulkner, E., “Tools for Environmental Monitoring and Response at Hydro Projects,”Hydro Review, April 2000, pp. 38-42.

FERC, Order Certifying Incremental Hydropower Generation for Production Tax Credit,Ameren Missouri, Project No. 459-301, January 19, 2011.

Foust, J. M., J. Etter, and R. K. Fisher, “Predicting Dissolved Oxygen and NitrogenUptake during Turbine Aeration,” Proceedings of HydroVision 2008, Kansas City,Missouri: HCI Publications, July 2008.

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8. AUTHOR

Patrick March is President and Principal Consultant for Hydro Performance ProcessesInc. (http://hydroppi.com), with over 35 years of hydropower experience. He is amember of the ASME’s Test Code Committee PTC-18 on Performance of HydraulicTurbines and Pump-Turbines, and he is a board member for the Hydro ResearchFoundation. Mr. March received his BS and MS degrees in Mechanical Engineeringfrom MIT, and he holds five patents for hydro-optimization and hydro-environmentaltechnologies. He has worked at MIT, Bolt Beranek & Newman, Alden ResearchLaboratory, and the Tennessee Valley Authority, where he was Director of the TVAEngineering Laboratory, Senior Manager of Hydraulic Engineering, and co-founder andGeneral Manager of Hydro Resource Solutions LLC.

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